One person complained that the description of the one-day delivery as free was misleading.

Amazon told the Advertising Standards Authority (ASA) that Prime provided a number of benefits to its members at a "clearly indicated cost" of £49 a year.

One of those benefits was free one-day delivery, which would usually cost between £3.95 and £7.99.

Amazon said it believed use of the word "free" to describe one-day delivery provided clarity about the benefits of the £49 annual fee.

But the ASA pointed out that advertisers must not describe part of a package as free if it is included in the overall price.

It said: "Although we understood Amazon's intention was to make clear that the one-day delivery could be used without charge after subscription, because members had to pay £49 before they could use the service we considered that the claim that one-day delivery was 'free' was misleading."

It added: "The claim must not appear again in its current form. We told Amazon not to describe Prime one-day delivery as free."